The invention herein relates generally to the art of studying the physical properties of particulate systems and more particularly is concerned with ascertaining accurately certain sizing information about a particulate system.
More specifically, the invention is concerned with obtaining information useful in industry and other processes where it is essential to describe the system by such highly significant statistical quantities as median size or mass as defined in the incorporated patent, and particle size which divides the number of particles in the system such that a predetermined percentage of the number of particles are smaller and/or larger than the selected size. The most useful dividing size will hereinafter be identified as the number or popululation median. That is, the size above and below which exit 50% by number of the particles in the particulate system. It is desireable to be able to ascertain this statistical information using the same equipment as previously used for ascertaining the mass median.
In the apparatus identified in U.S. Pat. No. 3,557,352 the particles in a particulate system are passed through a Coulter type of particle detector. Each particle causes a particle pulse to be developed whose amplitude is proportional to the size of the particle. As explained in greater detail in the above noted patent, size is related to mass so that the size of the particle pulse is related to the mass of the particle producing the particle pulse. The particle pulses produced by passage through the Coulter type particle detector are changed into representative electrical quantities, such as charges, which are proportional to the pulse amplitudes and hence, the respective size and mass of the particles themselves. These electrical quantities can be of a positive or a negative polarity depending on whether the particle pulse amplitude exceeds or falls below a variable threshold. The representative electrical quantities are passed to an accumulation circuit which builds up a charge that is related to the total number of charges coupled thereto, both plus and minus. The accumulating circuit will develop a signal which is related to the total charge thereon which is used to either manually adjust the threshold level of the threshold circuit, or is electrically fed back to the threshold circuit so that the positive and negative representative electrical quantities achieve a desired relationship with respect to one another. For example, the total charge accumulated will reach a point such that the threshold is adjusted to cause an equal number and amplitude of positive and negative charges to be coupled to the accumulating means. When they are equal the charge or voltage in the accumulating circuit will represent the size of particle which divides the system mass into predetermined fractions such as, for example, the mass median.
A second patent of interest to this application is U.S. Pat. No. 3,710,263 issued Jan. 9, 1973, and assigned to the same assignee as the patent which is incorporated by reference. In this patent a previous duration memory percentile responsive circuit is shown in FIG. 4 and described at columns 15 and 16. This circuit is substantially similar in configuration to a portion of the circuit shown in FIG. 6 of the incorporated patent. In the circuit shown in FIG. 4, of U.S. Pat. No. 3,710,263, pulses of varying width are coupled to the input. The circuit is operable to accumulate a representative electrical quantity, such as charge, of fixed amplitude and duration in response to each varying width pulse coupled thereto. These electrical quantities can be positive or negative depending on whether the pulse width exceeds or falls below a variable pulse width threshold. The quantities are passed to an accumulation circuit which builds up a charge related to the total number of charges received. This charge is converted to a voltage used to control the variable threshold and is a voltage representing the median duration of pulses coupled thereto. That is, there will be as many pulses greater in duration represented by the voltage as there will be pulses smaller in duration so that a voltage representative of the pulse width median is obtained.
Neither patent shows or describes apparatus capable of providing the statistical information of number median nor do they show or describe apparatus capable of providing either one of mass or number median.